Thermoforming Process of Plastic Making

Thermoforming sometimes called vacuum forming, is the shaping of hot sheets or strips of thermoplastic materials into a desired shape either by mechanical or pneumatic methods. The sheets of plastic used in the thermoforming process are produced by either extrusion, calendaring or pressing. Thickness of the sheets that are processed range from 0.125 to 3.2 mm or even greater.

The basic process is quite simple. A piece of plastic sheet is clamed into a frame. The plastic is heated, usually with electric heaters, until it begins to sag. Vacuum , air or mechanical pressure is then applied through small holes in the mold and the plastic is rapidly pulled tightly against the mold creating close profile conformity. The frame is raised, the part is removed and then trimmed in a punch press. The mold may have several shapes, for the same part or for different parts.

In vacuum forming, the sheet is clamped in a stationary frame and the heated sheet is vacuum-drawn into the mold.

A male mold is used in drape vacuum forming and a movable frame or clamp drapes a heat-softened sheet over the male mold before vacuum is pulled. A more complex shape can be developed by this method.

In the vacuum snap back process, in the first step , vacuum is produced in the chamber and the sheet is drawn down into the cavity. The male plug descends and clamps against the chase which holds the sheet. In the second step, vacuum is applied to male plug and the material is drawn to the mold. Deep drawn parts with generous tapers and corners with large radii are possible with this technique.

Among the items are made by thermoforming process are small jelly containers used in restaurants , luggage, refrigerator inner panels lighting fixture, helmets and containers for packing.

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